Obviously issues like poor technique, fitness, genetics and many other factors (perhaps bad luck) are a big part of injury proneness. As someone who seems to be a bit injury prone and has seen many injury prone footballers and tennis players through the years I find the subject to be very interesting. I'm not sure whether this belongs here or in the non-tennis forum,but here it is anyway.

Regularly stretching (20-30 mins 3 times a week) is supposed to be a huge help - and also a big factor in staying in shape and being nimble as you get older. However stretching before playing is not thought to be important anymore. Regular stretching resulting in greater flexibility/mobility is supposed to be the key. Of course, not everyone should follow the same stretching routine as all of our bodies are different. I'll try dig up an article I read recently on stretching and post it here.

As a side note(related to the second link above) if you look at Hewitt now, is this Nadal at age 27 too?